In wireless communication systems, many users communicate over a wireless channel. For example, code division multiple access (CDMA) modulation technique is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) may be used as well.
In a wireless communication, data may be modulated into symbols based on a modulation scheme. The symbols may then be spread into chips using one or more spreading codes. A wireless communication system may spread symbols using spreading codes with different spreading factors, where a spreading factor is the number of chips per symbol. For example, a universal mobile telecommunication system (UTMS) based wireless communication system may support communication protocols using different spreading factors. The communication protocols may include high speed downlink packet access (HSDPA) for high data rate transmissions, which has a spreading factor of 16, and release 99 (R99) for voice and data transmissions, which may have spreading factors of 2k with k between 2 and 8.
Because of the presence of multiple data transmissions for multiple users in a wireless communication system, it is desirable to mitigate multi-user interference (MUI) and inter-symbol interference, for example, along with noise. Traditionally, interference cancellation for different spreading factors is performed independently or performed jointly at the chip level. Chip-level interference cancellation is complex and may involve high-level algorithms and implementation tweaks. This complexity causes the receiver to be susceptible to error propagation. Therefore, systems and methods that provide accurate multi-user detection and interference cancellation in the presence of multiple spreading factors are desirable.